Infusion of clinical-grade enriched regulatory T cells delays experimental xenogeneic graft-versus-host disease

Background We investigated the ability of clinical-grade enriched human regulatory T cells (Treg) to attenuate experimental xenogeneic graft-versus-host disease (GVHD) induced by peripheral blood mononuclear cells (PBMNCs; autologous to Treg) infusion in NSG mice, as well as verified their inability to induce xenogeneic GVHD when infused alone. Study Design and Methods Human Treg were isolated from peripheral blood apheresis products with a cell separation system (CliniMACS, Miltenyi Biotec GmbH) using a two-step procedure (simultaneous CD8 and CD19 depletion followed by CD25-positive selection) in six independent experiments with six different healthy volunteer donors. Sublethally (2.5 Gy) irradiated NSG mice were given 2 x 10(6) cytapheresis (PBMNC) product cells intravenously (IV) without (PBMNC group) or with 1 x 10(6) Treg (PBMNC + Treg group), while other NSG mice received 2 x 10(6) enriched Treg alone (also in IV; Treg group). Results The first five procedures were successful at obtaining a relatively pure Treg population (defined as >50%), while the sixth procedure, due to a technical problem, was not (Treg purity, 42%). Treg cotransfusion significantly delayed death from xenogeneic GVHD in the first five experiments, (p < 0.0001) but not in the sixth experiment. Importantly, none of the mice given enriched Treg alone (Treg group) experienced clinical signs of GVHD, while, interestingly, the CD4+ cells found in these mice 26 days after transplantation were mainly conventional T cells (median CD25+FoxP3+ cells among human CD4+ total cells were only 2.1, 3.1, and 12.2% in spleen, marrow, and blood, respectively). Conclusions Infusion of clinical-grade enriched Treg delayed the occurrence of xenogeneic GVHD without inducing toxicity in this murine model.